The present invention relates to a roll charged with a heat transfer medium, such as a wringer roll used in iron manufacturing machine process facilities, a heating roll used in a continuous annealing furnace, or a hurst roll used in continuous annealing facilities.
In a conventional roll charged with a heat transfer medium, a heater 02 is arranged close to an internal surface of a roll body 01 so as to come in contact with a heat transfer medium 03 charged inside the hollow roll body 01 as shown in FIG. 7. Further, reference numeral 04 indicates a plate conveyed over the roll so as to undergo heat exchange with the roll.
Further, as shown in FIG. 8, in another conventional roll charged with a heat transfer medium, the heat transfer medium 03 is charged in a roll body 01, the central part of the roll body 01 is heated by means of a plate passed over the roll, and natural convection of the heat transfer medium 03 and turbulence of the flow of the heat transfer medium 03 caused by rotation of the roll body transfer heat in addition to thermal conduction of the roll body 01. This roll charged with a heat transfer medium is used as a wringer roll and the like for wiping molten salt from a steel plate.
In the above-described conventional roll charged with a heat transfer medium shown in FIG. 7, the heat transfer medium must be exposed to atmospheric air when the heater is open-circuited and needs to be replaced. As a result, the roll must be removed from a line without leakage of the heat transfer medium when changing the position thereof. Further, it becomes necessary to evacuate the inside of the roll body after replacing the heater when a heat transfer medium having a vapor pressure lower than atmospheric pressure at room temperature is charged. Thus, there are a great deal of maintenance costs associated with the roll.
Further, in this conventional roll charged with a heat transfer medium, a difference in temperature between a central contact portion and end portions of the roll body is produced in an axial direction of the roll by a thermal load applied by a plate having liquid attached thereto which is conveyed over the roll. Thus, a uniform heat exchange cannot be performed between the plate and the roll, and a thermal crown is produced on the roll due to a temperature difference existing in the axial direction of the roll. The pressure exerted on the plate by the roll is therefore non-uniform in the axial direction of the roll.
In particular, in a heater roll (wringer roll) used in a process line of iron manufacturing machines for wiping liquid from a steel plate at a high temperature, the roll temperature rises markedly only at the area of contact between the roll body and the steel plate in the axial direction of the roll as the steel plate at a high temperature passes thereby. The temperature of the roll at the end portions thereof remains low. Thus, the above-described problems are notable at the roll end portions. In addition, the temperature at the roll end portions becomes lower than the temperature at which the wiped liquid will solidify. As a result, there is such a drawback in that solidified matter accumulates at the roll end portions, which makes continuous operation impossible.
Further, when the above-described conventional roll charged with a heat transfer medium shown in FIG. 8 is used as a wringer roll, a temperature difference of approximately 200.degree. C. is produced in the roll body in the axial direction of the roll body, as shown with a curve A in FIG. 9, between a heated central part of the roll body in contact with the steel plate and at the end portions of the roll body out of contact with the plate. This temperature difference is caused by the thermal load of the plate when the plate passes over the roll and due to the fact that the heat transfer capacity of the charged heat transfer medium is high only in the circumferential direction of the roll because of the rotation of the roll, and the heat transfer capacity in the axial direction is small since heat transfer caused by the turbulence of the heat transfer medium flow and by natural convection only is generated in the axial direction of the roll. As a result, the roll body has such problems as a thermal crown being produced, thus lowering the performance of the roll in wiping the conveyed material and allowing the wiped liquid at the end portions of the roll to solidify.